Earth trenching machines for digging vertical wall trenches are well known as exemplified by U.S. Pat No. 4,230,372, and as disclosed in the parent application incorporated herein by reference. Typically, such equipment utilizes a rock saw unit having spaced apart saw wheels suitably supported for rotation from the end of an elongated boom contained on a crawler or track-type vehicle. Controls and adjustments provided on the vehicle enable the angle and depth of saw cut to be adjustably preset to accommodate immediate trenching needs.
As disclosed in the parent application hereof, saw wheels typically utilized for earth trenching include carbide cutting teeth and effectively produce parallel spaced apart side cuts leaving a center portion between cuts that is subsequently removed by means of a side chisel, explosive and/or crumbing shoe. All such equipment is known to operate well through relatively soft soil formations such a sand or even limestone, but have generally been inefficient and unsuitable for trenching through granite or other igneous hard rock. Not only must the hard rock be sawed through, but the problem is compounded by need to remove the center rock remaining between saw cuts. This has posed difficulty in the trade in that the need arises with some degree of frequency for trenching through such hard rock formations.
One instance where this has been encounted with particular concern is in long continuous trenching for long distance laying of fiberoptic cable. Customary trenching dimensions for cable laying are usually about four-four and one half inches in width to a depth of about twelve-eighteen inches. It is obviously preferred to be able to trench continuously without interruption, yet where a hard rock formation has been encountered using conventional saw units both delay and interruption have been incurred because of equipment failure. Despite recognition of the problem, suitable equipment for those purpose has not heretofore been known.